1. Field of the Invention
The present invention relates to an attachment device for an interchangeable optical device with a diaphragm mechanism.
2. Description of the Prior Art
In a conventional interchangeable optical device, such as an interchangeable lens, which is detachably mounted on a camera and is provided with a plurality of diaphragm blades to be opened and stopped down, a diaphragm interlocked member is provided to open and stop-down the diaphragm in response to information from the camera, with the diaphragm interlocked member being linked with a driving member provided in the camera when the interchangeable optical device is coupled with the camera. In such an interchangeable optical device of the structure as mentioned above, the diaphragm interlocked member is urged in a direction to open the diaphragm (hereinafter called opening tendency) or in a direction to stop-down the diaphragm (hereinafter called stopping-down tendency). In the case of the interchangeable lens having an opening tendency the driving member in the camera pushes the diaphragm interlocked member against the urging force to stop down the diaphragm. In the case of an interchangeable lens with the stopping-down tendency, the driving member in the camera pushes the diaphragm interlocked member to open the diaphragm fully in a normal condition. For stopping-down of the diaphragm, the driving member moves in the direction to go away from the diaphragm interlocked member allowing the latter to follow the driving member by the urging force and stop-down.
FIG. 1 shows an interchangeable lens with the stopping-down tendency, and FIG. 2 shows a diaphragm mechanism with the stopping-down tendency, provided in the interchangeable lens illurated in FIG. 1. With reference to those Figures the rear side of the interchangeable lens is shown as in the right side in the Figures. FIGS. 3 and 5 are the front view of diaphragm blades, respectively. The diaphragm mechanism comprises six diaphragm blades 8 (only one of them shown in FIG. 2.), which are supported between a restraining plate 11 and a diaphragm operating plate 5. Also, each diaphragm blade 8 carries pins 9 and 10 which are vertically extending in opposite directions from both sides of the diaphragm blade 8 but not being aligned with each other. The first pin 9 is received in a diaphragm driving cam slot 7 formed on the diaphragm operating plate 5, and the second pin 10 is received in a small hole formed on the restraining plate 11. A diaphragm interlocked member 3 extends from the diaphragm operating plate to the back of the interchangeable lens (to the right in FIG. 1) with its end projecting from the back of the interchangeable lens, as shown in FIG. 1.
In this structure, the diaphragm interlocked member 3 and the diaphragm operating plate 5 are urged by a spring 6 as shown in the FIG. 2 to turn in the counter-clockwise direction as viewed from the back of the interchangeable lens. When these members rotate under the force of the spring 6, diaphragm blades 8 will rotate counterclockwise about respective pins 10 to effect the stopping-down of the diaphragm.
When a male bayonet 2 of the interchangeable lens is fitted into a lens mount LM of a camera body CB and rotated clockwise relative to the camera body, the diaphragm interlocked member 3 will be brought into contact with a driving member DM of the camera body CB and moved in the clockwise direction as viewed from the rear of the lens to open the diaphragm fully.
When the diaphragm mechanism as described above is at the full open condition as illustrated in FIG. 3, only each adjacent two diaphragm blades overlap each other as seen in the cross-section in FIG. 4, so as not to interfere with one another. Conversely, when the diaphragm has been stopped down to the minimum aperture as shown in FIG. 5, more than three diaphragm blades overlap one another, engaging and interfering one another vigorously with the overlapping or engaging portions warping or curving. The smaller the minimum diaphragm aperture is, the more the blades interfere with one another.
When an interchangeable optical device having a diaphragm mechanism with the stopping-down tendency and a manual diaphragm setting means is detached from the camera with its diaphragm mechanism being preset to a minimum aperture, the diaphragm is stopped-down to and held at minimum aperture condition as shown in FIGS. 5 and 6. Thus, if the interchangeable optical device is kept in the detached condition for a long time, the diaphragm blades will become fatigued resulting in deformation of the blades. Also, vibrations caused while the interchangeable optical device set to the minimum aperture value is carried, may sometimes injure the diaphragm blades because of vigorous rubbing of the blades against one another. The rubbing of blades will also cause an anti-reflection paint coated on the surfaces of the diaphragm blades to come off little by little, so that the paint tips accumulate as dust inside the device. The deformation or injury of the diaphragm blades and the accumulation of the paint tips may cause malfunctions in diaphragm opening and stopping-down operation, resulting in incorrect diaphragm aperture size. Also, the damaged diaphragm blades may cause not only unexpected reflection of light at the injured surface but also adhesion of dust on the injured surface, resulting in deterioration of the optical performance of the device. These problems occur similarly in interchangeable optical devices having a diaphragm mechanism with the stopping-down tendency but having no manual diaphragm setting means. Consequently, it is desirable for the diaphragm to be kept open when not in use in the case of interchangeable optical devices having a diaphragm mechanism with the stopping-down tendency.
Japanese Utility Model laid-open Publication no. Sho 55-130312 discloses an interchangeable lens equipped with a means for opening the diaphragm when not in use. According to the Utility Model Publication, an interchangeable lens is provided with a cam member for determining the aperture size by controlling the amount of movement of the diaphragm blades. Besides an ordinary cam portion for setting the diaphragm aperture, the cam member is formed with an additional cam portion for opening the diaphragm larger than the minimum aperture when the interchangeable lens is detached from the camera body. Such interchangeable lens is designed such that it has a main body section, a mouth section, and a section including the cam member. The mounting and detaching of the interchangeable lens on and from the camera body can be performed by moving the main body section and the mount section relative to each other, and the section including the cam member is selectively coupled with one of the main body section and the mount section. When the interchangeable lens is mounted on the camera body, the section including the cam member is coupled through a clutch member to the main body section integrally therewith. At this time, a pin provided on the main body section enages the ordinary cam portion of the cam member to control the aperture. When the interchangeable lens is detached from the camera, the main body section is moved relative to the mount section. During this relative movement, the clutch member is switched such that the section including the cam member is connected integrally with the mount section. This may cause the pin provided on the main body section and the cam member to move relative to each other so that the pin engages the additional cam portion for opening the diaphragm larger than the minimum aperture.
The interchangeable lens of the construction as described above necessarily requires the body section and the mount section that move relative to each other upon mounting and detaching of the interchangeable lens to and from the camera body. The section including the cam member as well as the clutch member is also necessary. Thus, the interchangeable lens is extremely complicated in configuration. Also, it is practically impossible to modify a conventional interchangeable lens to employ therein the above construction because such modification requires drastic change of structure of the lens.